In conventional semiconductor packages that utilize 3D die stacking, the interconnect between the top and the bottom die usually has a very fine pitch on the order of 50 um or less. Due to this, an “underfill” material is used to protect the micro-solder joints in downstream assembly processes and in reliability testing. Capillary underfill (“CUF”) is one of the options used to accomplish this. It can be desirable to use CUF technology in the case of multiple top dies with narrow die to die spacing because of the so-called “keep-out zone” (“KOZ”) limitation of other underfill technologies such as dispensed epoxy flux or epoxy flux film. These technologies can require a greater KOZ than is desired for small die spacing.
Despite these advantages, however, CUF technology is limited by finite dispensing dot size and placement accuracy. As a result, a KOZ between the top die edge and the bottom die edge on the order of 500 um is usually required. In many application cases, however, the total die area of the top die is very close to the bottom die area, leaving very little space (e.g., 100 um or less) between the top and the bottom die edges. Dispense dot size reduction and equipment alignment accuracy improvement can help to reduce the size of the dispense KOZ. However, the run rate will be significantly lower because the same amount of underfill material is still needed and equipment upgrade is costly.
Reference will now be made to the exemplary embodiments illustrated, and specific language will be used herein to describe the same. It will nevertheless be understood that no limitation of the scope or to specific invention embodiments is thereby intended.